49 CFR § 386.51 - Amendment and withdrawal of pleadings.
(a) Except in instances covered by other rules, any time more than 15 days prior to the hearing, a party may amend his/her pleadings by serving the amended pleading on the Assistant Administrator or the administrative law judge, if one has been appointed, and on all parties. Within 15 days prior to the hearing, an amendment shall be allowed only at the discretion of the Administrative law judge. When an amended pleading is filed, other parties may file a response and objection within 10 days.
(b) A party may withdraw his/her pleading any time more than 15 days prior to the hearing by serving a notice of withdrawal on the Assistant Administrator or the Administrative Law Judge. Within 15 days prior to the hearing a withdrawal may be made only at the discretion of the Assistant Administrator or the Administrative Law Judge. The withdrawal will be granted absent a finding that the withdrawal will result in injustice, prejudice, or irreparable harm to the non-moving party, or is otherwise contrary to the public interest.